The rapid response of plasma metabolites to changes in feeding rate in a small passerine Wilsonia pusilla

Abstract

In order to apply plasma metabolite profiling to assess the quality of stopover habitat for migrant birds it is crucial to know how quickly metabolite concentrations change in response to variation in energy intake rate. We fed live mealworms to Wilson's warblers Wilsonia pusilla at rates designed to mimic a low quality (0.58 wet g/h) and a high quality (0.75 wet g/h) habitat. Plasma concentrations of triglycerides and B‐OH‐butyrate were higher and lower, respectively, on the high feeding rate, but plasma glycerol levels did not differ between feeding rates. Birds were then fed at the low rate for five hours, switched to the high rate and blood sampled at various times after the switch. Plasma triglycerides and B‐OH‐butyrate reflected the increase in feeding rate within 10 and 20 min, respectively. Plasma glycerol did not change significantly following the change in feeding rate. We conclude that plasma metabolite concentrations can change very quickly in response to variation in feeding rate, and thus provide a sensitive index of fueling rates near a capture site.

Obese super athletes: fat-fueled migration in birds and bats

“…Pectoralis muscles of migrating western sandpipers have an approximately 10-fold greater concentration of H-FABP (up to 11% of cytosolic protein) than that of mouse soleus muscle, and H-FABP has been shown to increase by 70% during migratory seasons compared with winter (Guglielmo et al, 2002a). H-FABP also increases during migration at the transcript level by up to 30-fold and at the protein level by ∼50% in the flight muscles of barnacle geese (Pelsers et al, 1999), wild and captive photostimulated white-throated sparrows (McFarlan et al, 2009;Zajac et al, 2011) and captive photostimulated yellow-rumped warblers (Dick, 2017). FAT/CD36 has been shown to increase at the transcript level by two to four times during migratory phases in wild and captive photostimulated white-throated sparrows, but protein changes could not be measured owing to a lack of antibody specificity (McFarlan et al, 2009;Zajac et al, 2011).…”

“…Studies of captive songbirds kept on constant diets also show that photoperiod changes alone are sufficient to induce changes in metabolic enzymes and fatty acid transporters in flight muscle (Dick, 2017;Zajac et al, 2011), so that when songbirds are in the migratory state they may not respond strongly or positively to dietary PUFA (i.e. they cannot go any higher).…”

“…Thus, if a flying bird exercises at nearly 80% VȮ 2,max , then the mammal crossover model would predict that only 5-10% of its energy would come from the oxidation of fatty acids delivered from adipose tissue to muscles through the circulation; however, the value is closer to 90% (Guglielmo, 2010). Flight muscles of migratory birds have very high activities of mitochondrial enzymes involved in fatty acid oxidation, such as hydroxyacyl-CoAdehydrogenase (HOAD) and carnitine palmitoyltransferase (CPT), that are greater in more migratory species (Lundgren and Kiessling, 1985), increase during migration seasons (Banerjee and Chaturvedi, 2016;Guglielmo et al, 2002a;Kiessling, 1985, 1986;Marsh, 1981;McFarlan et al, 2009;Zajac et al, 2011), and may increase at stopovers as birds refuel and prepare to depart (Driedzic et al, 1993;Maillet and Weber, 2007). However, increasing the mitochondrial fatty acid oxidation potential alone does not solve the problem with using adipose-derived fatty acids as fuel because the limitation in mammals appears to be due to constraints on transport through the circulation and uptake and transport of fatty acids by myocytes (Guglielmo, 2010;Vock et al, 1996).…”

“…H-FABP also increases during migration at the transcript level by up to 30-fold and at the protein level by ∼50% in the flight muscles of barnacle geese (Pelsers et al, 1999), wild and captive photostimulated white-throated sparrows (McFarlan et al, 2009;Zajac et al, 2011) and captive photostimulated yellow-rumped warblers (Dick, 2017). FAT/CD36 has been shown to increase at the transcript level by two to four times during migratory phases in wild and captive photostimulated white-throated sparrows, but protein changes could not be measured owing to a lack of antibody specificity (McFarlan et al, 2009;Zajac et al, 2011). In the same birds, FABPpm increased by fourfold and twofold at the transcript and protein levels, respectively, in wild migrants (McFarlan et al, 2009), but did not change at the transcript level in captive photostimulated sparrows .…”

“…2), the aerobic capacity of muscles and supporting systems must increase. This can be achieved in migratory birds by increasing flight muscle mass (Bauchinger et al, 2005;Guglielmo and Williams, 2003;Marsh, 1984;Piersma and van Gils, 2011), capillarity (Lundgren and Kiessling, 1988), mitochondrial volume (Evans et al, 1992), heart size (Bauchinger et al, 2005;Guglielmo and Williams, 2003;Piersma and van Gils, 2011), hematocrit (Piersma and Everaarts, 1996;Wingfield et al, 1990) and activities of the citric acid cycle and electron transport chain enzymes, such as citrate synthase (CS), malate dehydrogenase (MDH) or cytochrome oxidase (COX; Banerjee and Chaturvedi, 2016;DeMoranville, 2015;Dick, 2017;Driedzic et al, 1993;Guglielmo et al, 2002a;Kiessling, 1985, 1986;Maillet and Weber, 2007;Marsh, 1981;McFarlan et al, 2009;Zajac et al, 2011), and by decreasing anaerobic potential as indicated by muscle lactate dehydrogenase (LDH) activity (Banerjee and Chaturvedi, 2016;Dick, 2017;McFarlan et al, 2009;Zajac et al, 2011). Similarly, hoary bats were found to increase pectoralis muscle CS activity, shift lean body composition toward exerciserelated organs and have significantly larger lungs during migration (McGuire et al, 2013a,b).…”